A W7-X experiment program editor––A usage driven development

The set-up of experiment programs for the complex fusion device Wendelstein 7-X has to define a multitude of parameters which have to obey large number of rules arising from physics and technical constraints. Since this is hard to automate as long as the dependencies are not known sufficiently, the W7-X CoDaC team decided to implement an editor following a constructive approach: starting from an established experiment program the user is able to modify parts of it – thus complying the usual workflow of experimenters.Already the very first implementation has been deployed at the W7-X CoDaC prototype, the WEGA stellarator. Driven by agile programming principles the weighting of the requirements has been influenced by the editor usage in the daily experiment routine, thus ensuring client-oriented development steps and short release cycles. At present, a stable program editor implementation with graphical preview, immediate feedback on user actions and instantaneous warnings about incorrect settings is under continuous operation at the CoDaC prototype. It has potential to improve together with growing knowledge about the physical and technical constraints. The experiences gained give certainty that the editor is suitable for future use during the start-up phase and the first years of W7-X operation.     

MobileCoDaC – A transportable control,data acquisition and communication infrastructure for Wendelstein 7-X

MobileCoDaC is a test bed allowing in situ testing and commissioning the control and data acquisition of components to be operated at Wendelstein 7-X. It is a minimized replica of the functionality of the complete W7-X CoDaC infrastructure and can be operated independently.MobileCoDaC contains a set of W7-X CoDaC servers, network infrastructure, and accessories for remote access. All hardware is mounted in a single transportable rack system. Moreover, it provides the software infrastructure and user applications for experiment preparation, experiment operation, trouble shooting and experiment data access.MobileCoDaC has been operated successfully for test and commissioning of the control and data acquisition of the HEXOS (high efficiency extreme ultraviolet overview spectrometer) diagnostic at Forschungszentrum Jülich.     

Gate valve and shutter control system of the fusion experiment Wendelstein 7-X

The plasma vessel of the fusion experiment Wendelstein 7-X (W7-X) is a plasma vessel covering a plasma volume of about 30 m³. The vacuum conditions for plasma experiments inside the plasma vessel are supposed to be in a range of 1 × 10⁻⁸ mbar (ultra high vacuum conditions) after evacuation and conditioning. The 254 ports of the plasma vessel allow an external access to the inner space of the plasma vessel. Ports for heating and diagnostic systems are equipped with gate valves or with shutters. The vacuum gate valves are used as a controllable mechanical and a vacuum disconnection point between diagnostics and heating systems on the port side and the inner plasma vessel on the other side. The shutters are responsible for an optical and thermal protection for port windows or installed equipments inside the ports. After an overview of the main requirements for the control of the huge number of gate valves and shutters for the operational phases 1 and 2 of W7-X the design and realization of a centralized control system for controlling and observing all shutters and the majority of gate valves of the machine Wendelstein 7-X will be introduced and discussed.     

Designing and manufacturing of the coil support structure of W7-X

Wendelstein 7-X (W7-X) is a fully optimized low-shear stellarator and shall demonstrate the reactor potential of this fusion plant. It is presently under construction at the Greifswald Branch Institute of IPP. The superconducting magnet system will allow continuous operation, limited only by the plasma exhaust system whose capacity is designed for 30 min full power operation. The Wendelstein 7-X (W7-X) coils and structures are part of the largest superconducting fusion device being constructed at present. They represent a technical challenge at industrial level and the need for proven techniques and manufacturing processes in accordance to the highest quality standards. The production of these components requires a management of monitoring for quality and tests. The coil system consists of 20 planar and 50 non-planar coils. They are supported by a pentagonal 10 m diameter, 2.5 m high coil support structure (CSS). The CSS is divided into five modules. Each module consists of two equal half modules. The manufacturing status of the CSS and the main project management and technical challenges will be presented. The lessons learned in the large scale production of this difficult kind of support structure will be presented as relevant experience for the realization of similar systems for future fusion devices, such as ITER.     

Reverse engineering process of cryostat components of Wendelstein 7-X

The Wendelstein 7-X stellarator is a superconducting fusion experiment, presently under construction at the Greifswald branch of the Max-Planck-Institut für Plasmaphysik. This paper gives an overview of the reverse engineering processes applied on cryostat components of the W7-X superconducting magnet system.     

First experiences with the new W7-X like control system at the WEGA stellarator

The new quality of the superconducting fusion device Wendelstein 7-X (W7-X) is its capability of steady state operation. Additionally the fusion device W7-X is a very complex technical system. The modular and strongly hierarchical control system has been designed to cope with these two requirements unique for fusion devices.To minimize the risks before commissioning the control and data acquisition system at W7-X it will be thoroughly tested in a prototype installation at the WEGA stellarator. WEGA is a classical stellarator which allows steady state plasma pulses at a magnetic field of 0.5 T. Despite its lesser complexity WEGA has the same main components, e.g. magnetic coil systems, ECRH, and diagnostics as W7-X and is therefore considered to be a suitable test-bed for the control system.The installation of the new W7-X like control and data acquisition system has been finished in March this year. Individual components of the control system have already been commissioned during the installation phase. In April final commissioning and testing of the complete system took place. First discharges fully controlled by the prototype control system have been realized.The contribution will focus on first discharges controlled by the new system. Furthermore it presents first experiences that will incorporate into the further development of the control system and the tools for planning, preparation, and realization of plasma discharges.     

Probe manipulators for Wendelstein 7-X and their interaction with the magnetic topology

Probe manipulators are a versatile addition to typical plasma edge diagnostics.Equipped with material samples they allow for detailed investigation of plasma–wall interaction processes,such as material erosion,deposition or impurity transport pathways.When combined with electrical probes,a study of scrape-off layer and plasma edge density,temperature and flow profiles as well as magnetic topologies is possible.A mid-plane manipulator is already in operation on Wendelstein 7-X.A system in the divertor region is currently under development.In the present paper we discuss the critical issue of heat and power loads,power redistribution and experimental access to the complex magnetic topology of Wendelstein 7-X.All the aforementioned aspects are of relevance for the design and operation of a probe manipulator in a device like Wendelstein?7-X.A focus is put on the topological region that is accessible for the different coil current configurations at Wendelstein 7-X and the power load on the manipulator with respect to the resulting different magnetic configurations.Qualitative analysis of power loads on plasma-facing components is performed using a numerical tracer particle diffusion tool provided via the Wendelstein 7-X Webservices.     

Upgraded acceptance criteria from transient thermography control for the W7-X divertor target elements

The commissioning of plasma-facing component fields needs advanced non-destructive methods to detect in a reliable way the defects, which can impair the component performances and/or integrity during operation. Within this framework, CEA developed a dedicated non-destructive examination method based on active infrared thermography (SATIR facility) to inspect the bonding between armour material and metallic heat sink. Used with successful in the commissioning of the toroidal pump limiter of Tore Supra, this technique was applied in the frame of the pre-series activities of the Wendelstein 7-X high heat flux divertor elements to assess the bonding quality of the delivered components.This paper presents the methodology adopted to define an acceptance criterion based on SATIR test bed possibly applied for a serial inspection of the Wendelstein 7-X elements. Using the well-tried acceptance test based on the DTref_max parameter, the new method includes advanced data post-processing techniques from thermo-signal SATIR and a data merging method to help the decision-making and to optimise the reliability of the binary response expected for a final decision in terms of acceptance test.     

Piezo-valve controller for the gas inlet system of the fusion experiment Wendelstein 7-X

The gas inlet system of the fusion experiment Wendelstein 7-X (W7-X) comprises eleven gas inlets around the torus for controlled provision with working gases in the torus. This fast gas inlet system is designed for different operating modes of W7-X, from short discharges with only a few seconds durations to steady state plasma operation with operation time of 30 min. Piezo valves of type FGIS (FGIS: Fast Gas Injection System from General Atomics) are used as actuators for the W7-X gas inlet system.The design of an intelligent control unit for the FGIS Piezo valves are introduced and discussed. The integration of the valve controller units into the W7-X control component “W7-X gas inlet” and their planned application in an experiment run is described.     

Status of Wendelstein 7-X construction

Wendelstein 7-X (W7-X) represents the continuation of fusion experiments of the stellarator type at the Max-Planck Institute for Plasma Physics (IPP). The aim of W7-X is to demonstrate the suitability for a fusion reactor of this alternative type of magnetically confined plasma experiment. W7-X is being built at Greifswald in the northeast of Germany. The size of device (725 tons, height of 5 m, diameter 16 m) and the superconductive magnet system distinguish W7-X from earlier stellarators at IPP. The paper provides a summary of the status of the main components, the mastering of the technical challenges during component acceptance testing and during machine assembly. Latest results of the assembly work are especially highlighted. The scope of the construction of W7-X was modified and additional acceleration measures were implemented to mitigate risks and delays. Some aspects of these changes are explained in this paper.     

Analysis of the accident with the coolant discharge into the plasma vessel of the W7-X fusion experimental facility

Fusion is the energy production technology, which could potentially solve problems with growing energy demand of population in the future. Starting 2007, Lithuanian Energy Institute (LEI) is a member of European Fusion Development Agreement (EFDA) organization. LEI is cooperating with Max Planck Institute for Plasma Physics (IPP, Germany) in the frames of EFDA project by performing safety analysis of fusion device W7-X. Wendelstein 7-X (W7-X) is an experimental stellarator facility currently being built in Greifswald, Germany, which shall demonstrate that in the future energy could be produced in such type of fusion reactors. In this paper the safety analysis of 40 mm inner diameter coolant pipe rupture in cooling circuit and discharge of steam–water mixture through the leak into plasma vessel during the W7-X no-plasma “baking” operation mode is presented. For the analysis the model of W7-X cooling system (pumps, valves, pipes, hydro-accumulators, and heat exchangers) and plasma vessel was developed by employing system thermal-hydraulic state-of-the-art RELAP5 Mod3.3 code. This paper demonstrated that the developed RELAP5 model enables to analyze the processes in divertor cooling system and plasma vessel. The results of analysis demonstrated that the proposed burst disc, connecting the plasma vessel with venting system, opens and pressure inside plasma vessel does not exceed the limiting 1.1 × 10⁵ Pa absolute pressure. Thus, the plasma vessel remains intact after loss-of-coolant accident during no-plasma operation of Wendelstein 7-X experimental nuclear fusion facility.     

Real-time algorithms for JET hard X-ray and gamma-ray profile monitor

The steady state operation with high energy content foreseen for future generation of fusion devices will necessarily demand dedicated real-time tools and mechanisms for data handling and machine control. Consequently, the real-time systems for those devices should be carefully selected and their capabilities previously established. The Joint European Torus (JET) is undertaking an enhancement program, which includes tests of relevant real-time tools for the International Thermonuclear Experimental Reactor (ITER), a key experiment for future fusion devices. In these enhancements a new Data AcQuisition (DAQ) system is included, with real-time processing capabilities, for the JET hard X-ray and gamma-ray profile monitor. The DAQ system is composed of dedicated digitizer modules with embedded Field Programmable Gate Array (FPGA) devices. The interface between the DAQ system, the JET control and data acquisition system and the JET real-time data network is provided by the Multithreaded Application Real-Time executor (MARTe). This paper describes the real-time algorithms, developed for both digitizers’ FPGAs and MARTe application, capable of meeting the DAQ real-time requirements. The new DAQ system, including the embedded real-time features, was commissioned during the 2012 experiments. Results achieved with these real-time algorithms during experiments are presented.     

Configuration Management for Wendelstein 7-X

A complex system like the large superconducting Wendelstein 7-X stellarator necessitates a dedicated organizational structure which assures permanent consistency between the requirements of its system specification and the performance attributes of all its components throughout its life time. This includes well-defined processes and centrally coordinated information structures. For this purposes the department Configuration Management (CM) has recently been established at W7-X. The detailed tasks of CM for W7-X are oriented along common CM standards and comprise configuration identification, change management, configuration status accounting and configuration verification. While the assembly of W7-X is proceeding some components are still under procurement or even under design. Thus design changes and non-conformances may have a direct impact on the assembly process. Highest priority has therefore been assigned to efficient control of change and non-conformance processes which might delay the assembly schedule.     

Manufacturing and assembly status of main components of the Wendelstein 7-X cryostat

The stellarator fusion experiment Wendelstein 7-X (W7-X) is at present in assembly at the Max-Planck Institut für Plasmaphysik (IPP).The toroidal plasma with a ring diameter of 11 m and an average plasma diameter of 1.1 m is contained within the plasma vessel. Its form is dictated by the shape of the plasma. The form of the plasma is controlled by the coil system configuration. To control the plasma form it is necessary that all the 20 planar and 50 non-planar coils should be positioned within a tolerance of 1.5 mm. To meet this requirement a complex coil support structure was created, consisting of the central support ring and the different inter coil supports. The coils and the support structure are enclosed within the outer vessel with its domes and openings. The space between the outer and the plasma vessel is called cryostat because the vacuum inside provides thermal insulation of the magnet system, and the entire magnetic system is then be cooled down to 4 K. Due to the different thermal movements the plasma vessel and the central support ring have to be supported separately. The central support ring is held by 10 cryo legs. The plasma vessel supporting system is divided into two separate systems, allowing horizontal and vertical adjustments to centre the plasma vessel during thermal expansion.This paper aims to give an overview of the main components in the cryostat like the plasma vessel, the outer vessel, the ports and the different support systems. It describes the current manufacturing and assembly status and the associated problems of these components, using pictures and text. This paper does not describe the general assembly situation or time schedules of the Wendelstein 7-X.     

Common browsing and retrieval of technical and experimental data for steady state experiments

Steady state experiments like Wendelstein 7-X have to deal with large amounts of data of different kind. Discharge lengths may last from less than a second up to 30 min. During this time diagnostics will measure data in different discharge phases with different rates depending on the physical program. Furthermore the technical configuration of all devices must be logged during the discharge as well as between experiment phases. This is necessary to allow supervision of constantly running devices. All measured data must be stored together in a common database to make it easily accessible and reduce the effort to combine data. Because of these requirements a continuous data acquisition system must be provided where data may exist at any time. Intelligent methods for browsing and retrieval of the acquired data from the common database are desired. This includes calendar-based time interval selection, overview plots for intervals that cover several days and online views of the last stored data. The contribution will explain the challenges and the advantages induced by this kind of data access methods. Existing and planned solutions for Wendelstein 7-X will be depicted. Particularly the “Data Browser” – a graphical tool specially designed to fulfil these tasks at W7-X – will be presented.     

Configuration space control for Wendelstein 7-X

The Wendelstein 7-X stellarator (W7-X) is a superconducting fusion experiment, presently under construction at the Greifswald branch of the Max-Planck-Institut für Plasmaphysik. W7-X is a device with high geometrical complexity due to the close packing of the components in the cryostat and their complex 3D shape e.g. of the superconducting coils. The tasks of configuration space control are to ensure that all these components do not collide with each other under a set of defined configurations, i.e. at the time of assembly, at 4 K or for various coil currents. To fulfill these tasks sophisticated tools and procedures were developed and implemented within the realm of a newly founded division that focuses on design, configuration control and configuration management.     

Experiment planning using high-level component models at W7-X

The superconducting stellarator Wendelstein 7-X (W7-X) is a fusion device, which is capable of steady state operation. Furthermore W7-X is a very complex technical system. To cope with these requirements a modular and strongly hierarchical component-based control and data acquisition system has been designed.The behavior of W7-X is characterized by thousands of technical parameters of the participating components. The intended sequential change of those parameters during an experiment is defined in an experiment program. Planning such an experiment program is a crucial and complex task. To reduce the complexity an abstract, more physics-oriented high-level layer has been introduced earlier. The so-called high-level (physics) parameters are used to encapsulate technical details.This contribution will focus on the extension of this layer to a high-level component model. It completely describes the behavior of a component for a certain period of time. It allows not only defining simple value ranges but also complex dependencies between physics parameters. This can be: dependencies within components, dependencies between components or temporal dependencies.Component models can now be analyzed to generate various views of an experiment. A first implementation of such an analyze process is already finished. A graphical preview of a planned discharge can be generated from a chronological sequence of component models. This allows physicists to survey complex planned experiment programs at a glance.     

Processing of the quench detection signals in W7-X

The Wendelstein 7-X (W7-X) project uses superconductive coils for generation of the magnetic field to keep the plasma. One of the important safety systems is the protection against quench events. The quench detection system of W7-X protects the superconducting coils, the superconducting bus bar sections and the high temperature superconductor of the current leads against the damage because of a quench and against the high stress by a fast discharge of the magnet system.Therefore, the present design of the quench detection system (QDS) uses a two-stage safety concept for discharging the magnetic system. This paper describes the present design of the system assembly from the quench detection unit (QDU) for the detection of the quench to the quench detection interface (QDI) to implement the two-stage safety concept.     

Resource checking and event handling within the W7-X segment control framework

ITER, Wendelstein 7-X, LHD, and TORE SUPRA are experimental facilities designed to lead the way to steady state fusion devices. These experiments require strategies to sustain a discharge in case of unforeseen events, e.g. heat overloads of plasma facing components or the failure of a plasma heating source. A recovery strategy is needed to get the discharge back for physics exploitation. For this purpose the W7-X segment control framework provides means for automated event detection along with options to formulate and initiate a recovery strategy. Besides handling of failures and degradation there are events that represent a desired plasma physical effect. An example for this kind of event is a transition to from Low to High-Confinement mode. These events indicate that a certain plasma state is reached and scientific examination can be altered thus enabling event-driven multiple experiments per discharge. Examples of both kinds of events will be presented and compared to other approaches in the community.